The present invention relates generally to servo writing recording media disks. More particularly, the present invention relates to self-servo writing recording media disks having spiral servo tracks recorded thereupon.
Computer hard disk drives employ electromagnetic read/write heads to write and read data on the magnetic layers of one or more rotating disks. The data is stored on concentric data tracks on the disk surface. To guarantee the quality of the information saved on and read back from the disk, it is important to position the head at the center of the data track during both writing and reading. A closed-loop servo system is often used to accurately position the head on the data track using servo information embedded in a dedicated portion of each data track.
For such a servo system to operate properly, the servo information must be written to the data tracks with great position accuracy. Often the servo information is written on each surface as a set of spokes or wedges extending radially from the inner diameter of each disk. The portion of a servo wedge on each data track contains a sync field, an index mark, a gray-coded track number, and two or more fine-positioned offset bursts configured in an echelon across the data track. Head position relative to the center of a data track can be determined and corrected, if necessary, by reading and noting the respective amplitudes and timings of these offset bursts.
Traditionally, a machine called a “servo writer” is used to write the servo information to the disk. A servo writer includes a massive granite base to minimize the effects of vibration, precision fixtures to hold the disk drive, a precision laser interferometer-based actuator mechanism to place the head radially with respect to the axis of rotation of the disks in the drive, and an external clock head to position the servo wedges in time. These features cause present servo writers to be extremely large and expensive. And as the density of the tracks on the disk increases, the time required by the servo writer to write the servo data to the disk also increases, which can create a bottleneck in the disk drive manufacturing process at the servo writer. Because the time that a disk drive is being servo written is expensive, it is desirable to reduce the length of this costly process.
To reduce the time required by the servo writer, techniques called “self-servo writing” have been developed. A disk produced by one such technique, called “spiral servo,” is shown in FIG. 1. Instead of slowly writing the servo information to each concentric data track on each surface of each disk in a hard drive, the servo writer writes only a limited and much smaller number of spiral “servo tracks” (ST) having a known data pattern from the outer diameter (OD) to the inner diameter (ID) on only one surface of one of the disks by moving the head from OD to ID at a constant rate while the disk is spinning at a constant rate.
Then, without the aid of the servo writer, the hard disk drive uses timing information in the spiral servo tracks to determine the radial and circumferential position of the head, and writes conventional servo data to concentric data tracks on the disks using the hard drive's internal read/write head and servo system. Since the servo writer is used only to write the spiral servo tracks, the amount of servo-writing time on the servo writer is greatly reduced. The pattern on the disk surface after self servo writing is given in FIG. 2. The diagonal tracks are the residual spiral servo tracks ST, and the vertical strips represent the conventional servo spokes (SS). Once the self servo writing is finished, the spiral tracks are no longer needed, and can be overwritten by data tracks.